Calcium phosphate salts provide the hardness and rigidity which uniquely characterize normal, healthy bone and teeth. Developmental defects in the deposition of these salts or their destruction and loss by disease can severely impair the function of these skeletal tissues. The purpose of this project is to study the physical, chemical, and ultrastructural properties of these salts, and to clarify the kinetic and thermodynamic processes and the interactions with substances of biological interest that uniquely enable these salts to carry out their specialized role in vivo. The properties of calcium phosphate salts are being studied with a variety of ultrastructural and physical-chemical techniques such as electron microscopy, x-ray diffraction, surface area analyses, chromatographic and standard analytical chemistry procedures. The principal endeavor currently being pursued is the use of artificial lipid vesicles (i.e., liposomes) as in vitro models for investigating the physics-chemical aspects of calcium phosphate precipitate formation in matrix vesicles. The liposome experiments are being conducted with the goal of better understanding how matrix vesicles, the loci for early mineralization in many vertebrate hard tissues, can initiate precipitation in their membrane-bound interior spaces and control the expansion of this initial precipitate into the surrounding extracellular space. Present findings show (1) that the ability of high membrane cholesterol levels to interfere with transmembrane Ca fluxes necessary for initiating intraliposomal precipitation is independent of the phospholipid composition of the membrane, and (2) that the action of extraliposomal proteoglycans to control precipitate expansion involves both oligosaccharide as well as glycosaminoglycan components.